You want to make a solution at pH 4 by mixing acetic acid (Molar mass: 60.05 g/mol) with sodium acetate (Molar mass: 82.0343 g/mol) in 2L of water. You are told that your resulted solution should have a molarity of 0.9 M (including both acetic acid and sodium acetate). Please write down the acid-base equilibrium of acetic acid. Please calculate the mass of acetic acid and sodium acetate need to be added to 2L of water.